Twitter has lost a legal battle to try and trademark the word "tweet", despite it being the official word that describes the short messages issued via its micro-blogging service.

A direct result of the company's open API policy, something that has helped the site's arguably phenomenal growth, the US Patent and Trademark Office has ruled that three other companies already had prior claim on the word.

Twitter-related companies Tweetmarks, Cotweet and Tweetphoto had all applied for trademarks for their respective company names before Twitter itself did.

This ruling is likely a blow for Twitter, the co-CEO of which recently wrote in a blog post that they wanted to trademark the word not so others could not use it, but to protect it from abuse.

"We have applied to trademark Tweet because it is clearly attached to Twitter from a brand perspective but we have no intention of 'going after' the wonderful applications and services that use the word in their name when associated with Twitter", Biz Stone wrote on 1 July.

"In fact, we encourage the use of the word Tweet. However, if we come across a confusing or damaging project, the recourse to act responsibly to protect both users and our brand is important".